The anti-inflammatory effects of exercise training promote atherosclerotic plaque stabilization in apolipoprotein E knockout mice with diabetic atherosclerosis

Abstract

Physical exercise is the cornerstone of cardiovascular disease treatment. The present study investigated whether exercise training affects atherosclerotic plaque composition through the modification of inflammatory-related pathways in apolipoprotein E knockout (apoE(-/-)) mice with diabetic atherosclerosis. Forty-five male apoE(-/-) mice were randomized into three equivalent (n=15) groups: control (CO), sedentary (SED), and exercise (EX). Diabetes was induced by streptozotocin administration. High-fat diet was administered to all groups for 12 weeks. Afterwards, CO mice were euthanatized, while the sedentary and exercise groups continued high-fat diet for 6 additional weeks. Exercising mice followed an exercise program on motorized-treadmill (5 times/week, 60 min/session). Then, blood samples and atherosclerotic plaques in the aortic root were examined. A considerable (P<0.001) regression of the atherosclerotic lesions was observed in the exercise group (180.339 ± 75.613 x10(3)μm(2)) compared to the control (325.485 ± 72.302 x10(3)μm(2)) and sedentary (340.188 ± 159.108 x 10(3)μm(2)) groups. We found decreased macrophages, matrix metalloproteinase-2 (MMP-2), MMP-3, MMP-8 and interleukin-6 (IL-6) concentrations (P<0.05) in the atherosclerotic plaques of the exercise group. Compared to both control and sedentary groups, exercise training significantly increased collagen (P<0.05), elastin (P<0.001), and tissue inhibitor of matrix metalloproteinase-2 (TIMP-2) (P<0.001) content in the atherosclerotic plaques. Those effects paralleled with increased fibrous cap thickness and less internal elastic lamina ruptures after exercise training (P<0.05), while body-weight and lipid parameters did not significantly change. Plasma MMP-2 and MMP-3 concentrations in atherosclerotic tissues followed a similar trend. From our study we can conclude that exercise training reduces and stabilizes atherosclerotic lesions in apoE-/- mice with diabetic atherosclerosis. A favorable modification of the inflammatory regulators seems to explain those beneficial effects.

Figure 1

Glucose tolerance test results and the area under the curve (AUC) using the trapezoid rule. Comparisons were performed at each time point using one-way ANOVA, post-hoc Tuckey test. *P<0.05, exercise (EX) compared to control (CO) group; #P<0.05, EX compared to sedentary (SED) group.

Figure 2

A) Hematoxylin/eosin staining: representative examples of the effects of exercise on plaque size across the aortic arch, after; CO, control group; SED, sedentary group; EX, exercise group; the average plaque size in the aortic arch was significantly reduced in the exercise training group; scale bar: 400 µm. B) Orcein staining: exercise training significantly increased the elastin content of the atherosclerotic plaques and protected the integrity of internal elastic lamina (IEL); arrows point to ruptures of IEL; CO, control group; SED, sedentary group; EX, exercise group; scale bar: 400 µm. C) Exercise training significantly decreased MMP-8 content of the atherosclerotic plaques. CO, control group; SED, sedentary group; EX, exercise group; scale bar: 400 µm.

Figure 3

Representative examples of four serial sections of the aortic arch after staining with hematoxylin-eosin (A), orcein (B), MMP-3 (C), Sirius red (D), in a control mice. Scale bar: 400 µm.

Figure 4

Effects of exercise training on IL-6, MMP-2, MMP-3, MMP-8 and TIMP-2 content of the atherosclerotic lesions. CO, control group; SED, sedentary group; EX, exercise group. Results are expressed as mean ± standard deviation.*P<0.05, EX compared to CO group; #P<0.05, EX compared to SED group.